1. Field of the Invention
The present invention relates, in general, to equipment for cleaning steam generators and, in particular to an automatic sludge lance and method for cleaning sludge from steam generator tubes of a steam generator.
2. Description of the Related Art
In nuclear power stations, steam generators, such as recirculating steam generators and once-through steam generators, are used for heat exchange purposes in the generation of steam to drive the turbines. Primary fluid which is heated by the core of the nuclear reactor passes through a bundle of tubes in the steam generator. Secondary fluid, normally water, which is fed into the space surrounding the tubes, receives heat from the tubes and is converted into steam for driving the turbines. After cooling and condensation has occurred, the secondary fluid is directed back into the space around the tubes to provide a continuous steam generation cycle. Due to the constant high temperature and severe operating conditions, sludge accumulates on the lower portions of the tubes and on the tubesheet which supports same. The sludge which is mainly comprised of an iron oxide, such as magnetite, reduces the heat transfer efficiency of the tubes and can cause corrosion. Thus, the tubes must be cleaned periodically to remove the sludge. Various types of apparatus and method are available to accomplish this task.
U.S. Pat. No. 4,566,406 entitled "Sludge Removing Apparatus for a Steam Generator" discloses a manifold which is rigidly attached to the tubesheet and remain in place during conventional operation of the steam on the upper surface of the tubesheet. Openings are provided in the walls of the steam generator to remove the slurry.
U.S. Pat. No. 4,079,701 entitled "Steam Generator Sludge Removal System" discloses an arrangement of headers at the elevation of the sludge to be removed from around the tubes in order to establish a circumferential fluid stream at the elevation. A fluid lance moved along a line between the headers emits a fluid jet perpendicular to the line of movement of the fluid lance. The lance may also be rotated as it is removed.
U.S. Pat. No. 4,700,662 entitled "Sludge Lance Wand" discloses a lance for cleaning once-through steam generator tubes. The lance has a fixed radius of curvature thus necessitating manual manipulation of same in order to insert the lance between tubes within the tube bundle in the steam generator.
U.S. Pat. No. 4,980,120 entitled "Articulated Sludge Lance" assigned to the assignee of the present invention discloses an articulated lance for cleaning sludge located between steam generator tubes. In operation, the lance is inserted through a handhole into a lane or space between tubes in a tube bundle.
U.S. Pat. No. 5,194,217 entitled "Articulated Sludge Lance with a Movable Extension Nozzle" is also assigned to the assignee of the present invention and discloses an articulated sludge lance with a retractable movable extension nozzle.
In addition, U.S. Pat. No. 4,980,120 in the background art section describes various techniques found in U.S. Pat. Nos. 4,556,406, 4,079,701 and 4,700,662.
In addition to those references, U.S. Pat. No. 4,407,236 to Schukei, et al discloses a thin strip of spring steel which enters a tube lane for sludge lance cleaning for nuclear steam generators. The forward ends of the capillary tubes are directed downward for the jetting fluid under high pressure.
U.S. Pat. No. 4,827,953 to Lee is directed to an automated flexible lance for steam generator secondary side sludge removal. This patent discloses a flexible lance having a plurality of hollow flexible tubes extending lengthwise along the flexible member and remotely controlled inside the steam generator. There are a plurality of nozzles at an end of the flexible members with the flexible member being configured to go into the difficult to access geometry of the steam generator.
U.S. Pat. No. 5,065,703 to Lee describes improvements to the aforementioned automated flexible lance for steam generators.
U.S. patent application Ser. No. 08/126,453 filed Sep. 24, 1993 describes an articulated annular sludge lance.
Thus, there is still a need for a remote controlled automated sludge lancing method and apparatus which would position and manipulate the sludge lance in the steam generator and still have the drive assembly located outside the steam generator for easy accessibility. This would make the drive assembly readily serviceable and eliminate concerns of the harsh environment and space restrictions. Also, any loose parts would not damage the steam generator by being left inside. It is desirable for the apparatus and method to work from the no-tube lane and/or the annular chamber of the steam generator to provide the largest cleaning area possible.